The present invention relates to a tire having a radial carcass reinforcement, and more particularly to the sidewall and/or bead of such a tire.
French Patents FR 2 699 121 and FR 2 716 645 describe a tire having a radial carcass reinforcement of low H/S ratio, H being the height of the tire on its rim and S the maximum axial width thereof, which is intended to be mounted on a rim, at least one seat of which is inclined towards the outside and extended axially to the outside by a protrusion of low height. Said tire comprises at least one bead having the following characteristics:
a) the meridian profile of the center section of the carcass reinforcement is tangent to the anchoring bead wire of the carcass reinforcement at a point T such that the tangent TTxe2x80x2 forms with a line parallel to the axis of rotation of the tire an angle Ø, which is open radially and axially towards the outside, of at least 70xc2x0,
b) it is intended to be mounted on a rim such as described in the above patents, that is to say, one having the special characteristic of having at least one rim seat 42 inclined towards the outside, said seat 42 being extended axially to the inside either by a rim flange 44 or by the rim base on which is laid a tread bearing support, a lateral face of said support being used as the rim flange, and said seat being extended axially to the outside by a protrusion or hump 41 of low height;
c) the outer contour of the bead comprises (FIG. 1), axially to the inside, a wall 440 substantially perpendicular to the axis of rotation and may bear laterally on the axially inner flange 44 of the mounting rim J, said wall 440 of the bead B being extended axially to the outside by a frustoconical generatrix 430 which forms with a line parallel to the axis of rotation an angle xcex3 of 45xc2x0, which is open axially towards the inside and radially towards the outside, said generatrix 430 itself being extended axially to the outside by a second frustoconical generatrix 420 of the bead seat forming with the direction of the axis of rotation an angle xcex1 of 15xc2x0, which is open axially towards the inside and radially towards the outside. Said generatrix 420 is said to be inclined towards the outside, its axially outer end being on a circle of diameter less than the diameter of the circle on which its axially inner end is located. A frustoconical generatrix 410, extending the generatrix 420 axially to the outside and forming with the direction of the axis of rotation an angle xcex2 of 45xc2x0, which is open axially and radially towards the outside, completes the contour of the base of the bead B. A wall 450, of general orientation substantially perpendicular to the direction of the axis of rotation of the rim, finishes off the contour of the bead B. Whereas the generatrix 420 will bear on the rim seat 42, which is inclined towards the outside, the generatrix 410 will bear on the axially inner wall of the protrusion or hump 41 of the rim J, which is inclined by the same angle xcex2 as the generatrix 410. The bead thus defined is a bead, the heel of which is arranged axially to the inside, whereas the toe of the bead is arranged axially to the outside.
As the axially outer wall 450 is shown, that is to say set back axially relative to the axially outermost end of the rim, the type of tire thus described has the special characteristic of not protecting the axially outermost metallic elements of the rim against attack due to curbs when traveling in towns. Said problem is solved by adapting the axially outer form of the toe of the bead, this adaptation in the present case resulting in covering the outer protruding edge of the rim with a greater or lesser mass or protuberance of rubber of a suitable quality, the maximum axial width of the outer contour of the toe of the bead being greater than the space taken up or maximum axial width of the mounting rim.
Although said axially outer protuberance of the bead perfectly protects the corresponding protrusion of the rim, on the other hand it is very sensitive firstly to abrasion when the tire rubs against the curb, and secondly to fragments of rubber being torn off following the initiation and propagation of cuts and/or breaks.
The aim of the present invention is to minimize the consequences of attack by curbs on said protuberance.
To this end, and according to the invention, the axially outer protuberance of the bead is provided with incisions of a width other than zero, of a depth of at most 5 mm and arranged circumferentially parallel to each other.
Preferably, the width of the incisions will be between 0.5 and 5 mm, and they will be inclined relative to the radial planes corresponding to them and passing through the axis of rotation of the tire. The incisions will also advantageously be separated circumferentially at a pitch of between 1 mm and 5 mm.
At the same time as the reduction in sliding between the outer wall of a protuberance owing to the presence of numerous thin pieces of rubber, it would appear that the propagation of the degradation of the rubber mass is minimized by said presence, which results in a very clear reduction in the visual perception of the damage caused.
The characteristics of the present invention will be better understood with reference to the following description, which refers to the drawings illustrating in non-limitative manner an embodiment of the invention: